Systems and methods for controlling strobe illumination

ABSTRACT

Various exemplary embodiments may provide systems and methods for strobe illumination of a workpiece. The systems may include an illumination source, an image acquisition device and a control system. The illumination source may emit visible, UV, or near-IR light as a transient flash to the workpiece, the transient flash occurring in response to a lamp trigger. The illumination source may emit the light at an illumination intensity that rises from a begin threshold to a peak and afterwards diminishes to an end threshold during a flash duration. The image acquisition device may capture the light associated with the workpiece for an exposure duration starting from an exposure trigger. The control system may control the illumination source and the image acquisition device to synchronize the lamp trigger so that the exposure duration ends during the flash duration, such that a remaining portion of the flash does not affect the image exposure.

BACKGROUND

This invention relates to systems and methods that select light sourcechannels and control light intensity and direction for precision machinevision inspection using a transient light source.

Methods for operating a machine vision inspection system with a cameraand a stage that are movable relative to one another to focus on andinspect selected features of a workpiece on the stage are generallyknown. Precision machine vision inspection systems may be used to obtainprecise dimensional measurements of inspected objects and to inspectvarious other object characteristics.

Such systems may include a computer, a camera and/or optical system anda precision stage that may be movable in multiple directions to allowthe camera to scan the features of a workpiece that is being inspected.One exemplary prior art system, of a type that may be characterized as ageneral-purpose “off-line” precision vision system, is the commerciallyavailable Quick Vision™ series of vision inspection machines and QVPak®software available from Mitutoyo America Corporation (MAC), located inAurora, Illinois.

Such general-purpose “off-line” precision vision systems often include aprogrammable illumination system and a lens turret with lenses ofvarious magnifications, for example, to increase versatility of theimage systems and provide the ability to rapidly change configurationand imaging parameters for the vision systems to perform a wide varietyof inspection tasks. There is a common need to inspect various types ofobjects or inspection workpieces, or various aspects of a singleworkpiece, using various combinations of magnifications and theprogrammable illumination settings.

General purpose precision machine vision inspection systems, such as theQuick Vision™ system, are also generally programmable and operable toprovide automated video inspection. Such systems may include featuresand tools that simplify the programming and operation of such systems,such that operation and programming may be performed reliably by“non-expert” operators. For example, U.S. Pat. No. 6,542,180, which isincorporated herein by reference in its entirety, teaches a visionsystem that uses automated video inspection. The system performsoperations to adjust the lighting used to illuminate a workpiece featurebased on a plurality of selected regions of a feature image.

Imaging systems are widely used to inspect workpieces being transportedthrough a manufacturing process. Equipment such as machine visioninspection systems often capture images of the workpieces using acamera, for example, and process captured images to verify variousworkpiece dimensions by identifying edges of relevant features in theimages.

SUMMARY

The precise location and repeatability of where an edge is detectedwithin an image depends on the lighting of the workpiece during imagecapture. Edge artifacts or edge-shifting may be created bylighting-specific shadows cast due to sub-optimal direction of theillumination of the workpiece. Over- or under-exposure may reduce theability to accurately detect an edge, and decrease measurementrepeatability. To increase productivity, workpieces may be kept inmotion, even during image capture. This places an additional burden onillumination systems to minimize blurring caused by the motion. Suchfactors frequently limit the accuracy with which the edge of a featuremay be located within an image and/or the velocity that may be toleratedduring image capture. Thus, improvements in workpiece illuminationcontrol technology would be very desirable.

Various exemplary embodiments provide systems and methods for strobeillumination for imaging a workpiece. Exemplary systems may include anillumination source, an image acquisition device and a control system.The illumination source may emit light of one or more visible orinvisible wavelengths of radiation that are suitable for imaging theworkpiece, as a transient flash or pulse to the workpiece. The transientflash or pulse may occur in response to a lamp trigger. The illuminationsource may emit the light at an illumination intensity that rises from abegin threshold to a peak and afterwards diminishes to an end thresholdduring a flash duration. The image acquisition device may capture thelight associated with the workpiece for an exposure duration started inresponse to an exposure trigger. The control system may control theillumination source and the image acquisition device to provide adesired overlap between the exposure duration and the flash duration.The beginning of the exposure duration may precede the lamp trigger by alamp lag period. The lamp trigger may be set to synchronize or adjust atiming relationship between an end of the exposure duration and theillumination intensity profile of the flash.

In various exemplary embodiments, exposure triggers may correspond topredetermined positions of the workpiece relative to a coordinate spaceused by the machine vision inspection system.

In various exemplary embodiments, such a system may further include aspatial light modulator (SLM) that forms an array to control and/ordistribute the light from one or more illumination sources. The arraymay include elements that selectively either block, partially transmit,or transmit the light toward respective lighting channels, such asrespective optical fiber bundles. Each respective lighting channel maydirect the light along a path to project commanded illumination from arespective position and/or angle of incidence relative to the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

Various details are described below with reference to the followingfigures, wherein:

FIG. 1 shows a diagram of an exemplary general purpose machine visioninspection system;

FIG. 2 shows a block diagram in greater detail of a control system, avision components system and a light source system of the exemplarymachine vision inspection system;

FIG. 3 shows a block diagram in greater detail of the light sourcesystem and a lighting control interface;

FIG. 4 shows an exemplary graphical user interface of a control for aspatial light modulator;

FIG. 5 shows a schematic layout diagram of exemplary lighting systemincluding a spatial light modulator;

FIG. 6 shows a bar-chart of exemplary relative grayscale intensitiesobtained when imaging various materials at different magnifications;

FIG. 7 shows a timing diagram of exemplary camera and flash triggersassociated with strobe illumination and exposure control;

FIG. 8 shows a block diagram of an exemplary controller signalsassociated with a light generator and a vision measuring machine;

FIG. 9 shows a schematic layout diagram of exemplary light channels,including a structured light channel and a spatial light modulator;

FIG. 10 shows a plot illustrating exemplary generic relationshipsbetween a power setting and corresponding strobe duration times; and

FIG. 11 is a flowchart illustrating an exemplary method of using astrobe light source and a spatial light modulator to provideillumination levels for one or more light sources.

DETAILED DESCRIPTION OF EMBODIMENTS

The following detailed description refers to multi-channel strobeillumination for magnified image acquisition. The strobe illuminationsource may refer to a Xenon flashlamp, for example. However, theprinciples described herein may be equally applied to any known orlater-developed transient illumination sources, beyond the examplesspecifically discussed herein.

Exemplary systems and methods for machine vision inspection, as providedherein, may be used in conjunction with systems and methods disclosed inU.S. patent application Ser. No. 10/719,210 filed on Nov. 24, 2003directed to automatic focusing, and/or U.S. patent application Ser. No.10/901,355 filed on Jul. 29, 2004 directed to strobe illumination,and/or U.S. patent application Ser. No. 10/435,625 filed on May 7, 2003directed to improved machine vision inspection throughput, each of whichis incorporated herein by reference in its entirety.

Various methods and GUIs usable for determining an optimum light settingto be used with rapid auto focus systems that determine an estimatedbest focus position and associated light adjusting systems are disclosedin U.S. Pat. Nos. 6,542,180 and 6,239,554, each incorporated herein byreference in its entirety. In addition, techniques for measuring surfacecontours are disclosed in U.S. Pat. No. 6,690,474, also incorporatedherein by reference in its entirety.

FIG. 1 is a block diagram of an exemplary embodiment of a generalpurpose programmable machine vision inspection system 10 usableaccording to this invention. The machine vision inspection system 10 mayinclude a vision measuring machine 200 that may be operably arranged toexchange data and control signals with a control system portion 120.

The control system portion 120 may be further operably arranged toexchange data and control signals with at least one of a monitor 136 a,a printer 136 b, a joystick 138 a, a keyboard 138 b, and a mouse 138 c .The vision measuring machine 200 may include a moveable workpiece stage210 and an optical imaging system 205, which may include a zoom lens ora number of interchangeable lenses. The zoom lens or interchangeablelenses may generally provide various magnifications for images producedby the optical imaging system 205.

The joystick 138 a maybe used to control the movement of the movableworkpiece stage 210 in both X- and Y-axes horizontal directions, whichmay be generally parallel to the focal planes and perpendicular to theZ-axis movement direction of the optical imaging system 34. Frequently,Z-axis movement may be controlled by a rotary deflection component of ahandle or knob of the joystick 138 a. The joystick 138 a may be providedin a form other than that shown, such as any visual representation orwidget on the monitor 136 athat may be intended to function as a“virtual motion control device” of the machine vision inspection system10 and is controllable through any computer input device, such as themouse 138 c or other analogous devices.

FIG. 2 shows a detailed block diagram of a machine vision inspectionsystem 10′, which is an exemplary embodiment of the machine visioninspection system 10, that includes the control system portion 120, thevision measuring machine 200 and, in addition, includes a controllablelight generation system 300. The control system portion 120 may bearranged to exchange data and control signals with both the visionmeasuring machine 200 and the light generation system 300.

The control system portion 120 may include a controller 125 that may bein communication with, or connected to, an input/output interface 130, amemory 140, a workpiece program generator and executor 170, acomputer-aided design (CAD) file feature extractor 180 and a powersupply portion 190. The control system portion 120 may also be arrangedto exchange data and control signals with display devices 136 and inputdevices 138, for example, through the input/output interface 130.

The input/output interface 130 may comprise an imaging control interface131, a motion control interface 132, a lighting control interface 133,and a lens control interface 134. The motion control interface 132 mayinclude a position portion 132 a and a speed and acceleration portion132 b. The lighting control interface 133 may include lighting channelexposure and control portion 135.

The various elements of the control system portion 120 may generallyencompass hard-wired circuits, software circuits, subroutines, objects,operations, application programming interfaces, managers, applications,or any other known or later-developed hardware or software structure.The display devices 136 may include, for example, the monitor 136 a andthe printer 136 b (FIG. 1). The input devices 138 may include, forexample, the joystick 138 a, the keyboard 138 b and the mouse 138 c(FIG. 1). In general, the various elements of the control system portion120, may be operably connected to each other and to external devices byany suitable known or later-developed power and/or signal busses,wireless communication signals, and/or application programminginterfaces, or the like. Such interconnections are generally indicatedby various interconnection lines 195, throughout the control systemportion 120, in an arrangement of interconnections that is exemplaryonly, and not limiting.

The light generation system 300 may include one or more light generator310 and a spatial light modulator (SLM) 350 to control the distributionof light from the light generator 310, to a plurality of light channels,as described further below. The light generator 310 and the SLM 350 maybe arranged to exchange data and control signals with the light channelexposure and control portion 135, for example, by respective power andsignal lines 311, 351. At least one of the lamps (not shown) of thelight generator 310 maybe used in a strobe illumination mode ofoperation to provide a combination of a very fast light generatorresponse time (in the As or ns range) and suitable optical power levels.In various exemplary embodiments, the light generator 310 may include ahigh intensity Xenon (Xe) flashlamp. However, in general, any lightgenerator that emits a wavelength within a sensing range of the camera260 may be used. Various features of the light generation system 300 aredescribed further below.

The vision measuring machine 200 may include an optical assembly 205,light sources, including stage light source 220, coaxial light source230, and programmable ring light (PRL) source 240. The workpiece stage210 may include a central transparent portion 212 through which lightfrom the stage light source 220 passes. The stage 210 may becontrollably movable along X- and Y-axes that lie in a planesubstantially parallel to the surface of the stage 210 where a workpieceor target 20 may be positioned.

The stage light source 220 may receive light through a light cable 221from a respective channel of the SLM 350 to transmit light 222 throughthe transparent portion 212. The components that provide the light 222may be regarded as a first light channel of the machine visioninspection system 10′. The coaxial light source 230 may receive lightthrough a light cable 231 from a respective channel of the SLM 350 totransmit light 232 to a beamsplitter that provides a coaxial mirror 233that directs the transmitted light 232 through the objective lens 250.The components that provide the light 232 may be regarded as a secondlight channel of the machine vision inspection system 10′. Theprogrammable ring light (PRL) source 240 may form an annular ring aboveand around the workpiece 20 to transmit light 242 to the workpiece 20 atcontrollable angles. An exemplary configuration for the PRL source 240may include four ring-light sources 240 a. Through 240 d, arranged inrespective quadrants around the ring-light. The four sources 240 a.Through 240 d may receive light through respective light cables 241 a.Through 241 d from respective channels of the SLM. 350. The variouslight cables may comprise optical fiber bundles, or the like. The PRLsource 240 may be formed as a combination of individually controllablesources. The components that provide respective portions of the light242 may be regarded as four additional light channels of the machinevision inspection system 10′.

The workpiece 20 may be disposed on the stage 210 at a known or learnedposition. By detecting macroscopic positions of the stage 210 and/or theworkpiece 20, the control system portion 120 may accurately determinewhere to capture workpiece images to perform inspection of variousworkpiece features.

The memory 140 may comprise an image file memory portion 141, aworkpiece program memory portion 142, and a video tool portion 143. Thevideo tool portion 143 may comprise a region of interest generator 143x, and various respective video tools 143 a. Through 143 m, which mayinclude respective GUI interfaces, image processing operations, and thelike, which assist a user in performing and/or programming variousinspection operations. The region of interest generator 143 x providesoperations that may assist the user in defining desired regions ofinterest to be analyzed or operated upon be the various video tools 143a-143 m, as described in the '180 patent, for example.

The memory 140 may store data and/or “tools” usable to operate themachine vision inspection system 10 to capture or acquire an image ofthe workpiece 20 with desired image characteristics. The memory 140 mayfurther store data and/or video tools usable to operate the machinevision inspection system 10 to perform various inspection andmeasurement operations on the acquired images, either manually orautomatically, and to output the results, for example, through theinput/output interface 130 through data and/or control busses and/or thecontroller 125. The memory 140 may also contain data defining a GUIoperable through the input/output interface 130 by way of data and/orcontrol busses and/or the controller 125.

The optical assembly 205 may include, for example, a camera or imageacquisition device 260, an interchangeable objective lens 250, a turretlens assembly 280, and the coaxial light source 230. The objective lens250 and the camera 260 may be aligned along a camera axis. The opticalassembly 205 may be controllably movable along the Z-axis that isgenerally orthogonal to the X- and Y-axes, for example, by using acontrollable motor 294. Each of the X-, Y- and Z-axes of the machinevision inspection system 10 may be instrumented with respective X-, Y-and Z-axis position encoders (not shown) that provide spatial positioninformation to the control system portion 120, for example, oversuitable signal and/or control lines (not shown). The camera 260 mayinclude a charge-couple diode (CCD) array, or a CMOS array, or any othersuitable detector array, to provide an image based on the light receivedfrom the workpiece 20.

The turret lens assembly 280 may include two or more respective lenses286, 288 that may be rotated around a rotation axis 284 to berespectively positioned in the optical path between the camera 260 andthe objective lens 250 to provide a respective image magnification incombination with the objection lens 250. The control system portion 120may rotate the turret lens assembly 280 to provide a desired imagemagnification. The input/output interface 130 may exchange data andcontrol signals with the camera 260, the turret lens assembly 280 andthe motor 294, for example, by power and signal lines or busses 262,281, 296. Respective signal and/or control lines (not shown) of therespective X-, Y- and Z-axes position encoders (not shown) may also bein communication with the input/output interface 130. In addition tocarrying image data, the signal line 262 may carry various signals fromthe controller 125 that set an image acquisition pixel range for thecamera 260, initiate an image acquisition camera operation sequence,and/or similar operations.

The optical assembly 205 of the machine vision inspection system 10 mayinclude, in addition to the previously discussed components, otherlenses, and/or other optical elements, such as apertures, beam-splittersand other analogous devices, such as may be needed for providingdesirable machine vision inspection system features.

The workpiece 20 to be imaged and inspected using the machine visioninspection system 10 may be placed on the stage 210. One or more of thelight sources 220, 230, 240 may emit the respective light 222, 232, 242,that may illuminate the workpiece 20. Light may be reflected from ortransmitted through the workpiece 20 as workpiece light 255, which maypass through the interchangeable objective lens 250 and one of thelenses 286, 288 of the turret lens assembly 280 to be received by thecamera 260. The image of the workpiece 20, captured by the camera 260,may be output, for example, through the signal line 262 to the controlsystem portion 120.

A distance between the stage 210 and the optical assembly 205 may beadjusted to change the focus of the image of the workpiece 20 capturedby the camera 260. For example, the optical assembly 205 may be movablein the vertical (Z-axis) direction perpendicular to the stage 32, forexample, using the controllable motor 294 that may drive an actuator, aconnecting cable, or other analogous devices, to move the opticalassembly 205 along the Z-axis. The term Z-axis, as used herein, refersto the axis for focusing the image obtained by the optical assembly 205.The controllable motor 294, when used, may be in communication with thecontrol system portion 120, for example, through the signal line 296.

The control system portion 120 may be usable to determine imageacquisition settings or parameters and/or acquire an image of theworkpiece 20 with desired image characteristics in a region of interestthat includes a workpiece feature to be inspected by workpiece programinstructions. Such workpiece imaging instructions may be encoded by theworkpiece part programming generator and executor 170 and transmitted toother components through data and/or control busses and/or applicationprogramming interfaces 195. The display devices 136 and input devices138 may be used to view, create and/or modify part programs, to view theimages captured by the camera 260, and/or to view and/or modify variousGUI features for monitoring and/or controlling the machine visioninspection system 10′. The physical movements may be controlled by themotion control interface 132.

To achieve control of the physical movements of the camera 260, themotion control interface 132 may receive position information from theX-, Y- and Z-axis position encoders and may transmit position alteringcontrol signals via data and/or control busses and/or applicationprogramming interfaces 195. In general, such. instructions may cause themachine vision inspection system 10′ to manipulate the stage 210 and/orthe camera 260 such that a particular portion of the workpiece 20 may bewithin the field of view of the camera 260 and may provide a desiredmagnification, a desired focus state and an appropriate illumination.This process may be repeated for each of multiple images in a set ofimages that are to be captured for inspecting the workpiece 20.

FIG. 3 shows an exemplary block diagram of details of the lightingcontrol interface 133 including the light channel and exposure controlportion 135, and the light generation system 300. The light channel andexposure control portion 135 may include a timing and synchronizationportion 135 a, an SLM control portion 135 b and a light generatorcontrol portion 135 c. The SLM control portion 135 b may be connected tothe SLM 350, for example, through a signal line or buss 351. The lightgenerator control portion 135 c may be connected to the light generator310, for example, through a power and/or signal line or buss 311.

The light generator 310 may emit light 314 to illuminate an illuminationarea 315 on the SLM 350. The SLM 350 may generally transmit, partiallytransmit, or block light. The SLM 350 may include a plurality ofrespective controllable apertures within the illumination area 315. Therespective apertures may generally provide illumination control for therespective light channels of the machine vision inspection system bytransmitting, partially transmitting, or blocking the light 314 to eachof the respective light channels. In the example shown in FIG. 3, theapertures include a stage light channel aperture 321, a coaxial lightchannel aperture 331, and PRL light channel apertures 341 a, 341 b, 341c, 341 d. The respective apertures 321, 331, 341 a-341 d mayindividually control the amount of light 314 transmitted to therespective light cables 221, 231, 241 a-241 d (FIG. 2) to be outputthrough the respective light sources 220, 230, 240 a-240 d.

The SLM 350 may include an arrangement of shutters that provide therespective apertures. The shutters may be of any now-known orlater-developed type that can provide controllable light transmittingand light blocking functions in a desired pattern. In variousembodiments, it may be advantageous if the shutter may also be used topartially-transmit light. For example, such that the SLM may be used toselectively transmit, attenuate and/or block light from the lightgenerator 310. One example of such an SLM may be a micro-displaygraphics array from CRL-Opto in Dunfermline, Scotland, United Kingdom,which includes an LCD pixel array that may generally be controlled byconventional video signals, if desired, and may be used to display anelectronically generated 8-bit gray-scale pattern that may transmit,partially-transmit, or block the light 314 through any given pixel ofthe pattern, depending on its gray-scale value. In such a case, thevarious respective apertures may be implemented as features of thepattern, and the pattern may be controlled at conventional video rates.Alternatively, a custom LCD including a custom pattern of desiredapertures may be used in various embodiments. It should be appreciatedthat the SLM 350 allows one light generator 310 to provide independentlycontrollable lighting to a plurality of light channels, while alsoallowing the light from a plurality of light channels to be perfectlysynchronized, for example as one light generator 310 is strobed duringan image acquisition. The use of one light generator 310 also allowsreduced cost and reduced size, relative to the use of an individuallight generator for each light channel, for example.

Alternatively, the SLM 350 may include an arrangement of any now-knownor later-developed type of controllable reflective shutters that canprovide controllable light deflection in a desired pattern. In such acase, the light generator 310 may be arranged such that the light 314will not reach the various light channels unless the controllablereflective shutters or pixels “transmit” the light by reflecting and/ordeflecting light at a specific angle toward the various light channels.For example, in contrast to FIG. 3, the reflective SLM may be nominallyoriented along a plane at 45 degrees relative to the light 314, and thereflective array elements may be aligned along that plane to transmitthe light 314 toward the various respective light channels by reflectingand/or deflecting it at a right angle to reach the various respectivelight channels. To effectively “block” the light 314 from reaching thevarious light channels, the reflective array elements or pixels may bedisabled from reflecting the light 314 at right angles, either byaltering their individual angles, of by blocking their individualreflective light paths, for example using individually controllable LCDblocking elements. Examples of controllable reflective shutter arraysthat may be used include liquid crystal on silicon (LCOS) micro-displayproducts, for example, from CRL Opto, Dunfermline, Scotland, and digitallight projector (DLP) micro-mirror products, for example, from TexasInstruments DLP Products, Plano, Tex. In such a case, the variousrespective apertures may be implemented as features of a reflectivepattern, and the pattern may be controlled at conventional video rates.Although the micro-mirror type of devices may not providepartially-transmitting pixels, it will be appreciated that a lightchannel aperture implemented using a micro-mirror device mayalternatively attenuate the light transmitted to a particular lightchannel by effective reducing the its aperture size, as needed. Forexample, the aperture diameter may be reduced by altering theconfiguration of the pixels that form the aperture.

As previously outlined, it may be advantageous if at least one of thelamps of the light generator 310 may be used in a strobe illuminationmode of operation to provide a combination of a very fast lightgenerator response time (in the μs or ns range) at suitable opticalpower levels. Such illumination is particularly advantageous forallowing imaging of workpieces while continuing to move the stage 210(FIG. 2), which increases the throughput of the machine vision system10′. One example of a light generator 310 may include one or more highintensity light emitting diodes (LEDs), such as one of the LEDs in theLuxeon™ product line, available from Lumileds Lighting, LLC, of SanJosé, Calif., which may be used for both continuous wave (CW) and strobeillumination as described in U.S. patent application Ser. No. 10/719,210In various exemplary embodiments, a CW light source may include a highintensity discharge (HID) metal halide lamp and/or a quartz halogenlamp.

In various exemplary embodiments, the strobe light generator may includea high intensity Xenon (Xe) flashlamp, such as model CX-1500 Xeflashlamp of the CX-Strobe series from PerkinElmer® Optoelectronics ofFrémont, Calif. The CX-1500 Xe flashlamp may illuminate across anelectromagnetic spectrum for wavelengths between 250. nm and more than1100 nm. In various embodiments, it may be desirable to filter the lightfrom the flashlamp, to reduce heating and/or chromatic aberrations. Forexample, the filter may pass the visible wavelength range between 390 nm(violet) and 750 nm (red) to the light channels. However, in variousembodiments, other wavelengths ranges may be desired. The CX-1500 Xeflashlamp may cycle at a repeat rate of between 16 Hz and 35 Hz, with apulse duration of between 8 μs and 10 μs. The CX-1500 Xe flashlamp mayproduce a radiometric output of 256 mJ and a photometric light output of205 lumen-sec at 600 VDC that may be directed into a 0.9″ (23 mm)diameter fiber optic guide.

It should be appreciated that a general purpose machine vision systemmay image a wide variety of workpieces, some of which may have surfaceswith low reflectivity. Furthermore, magnified images may be desired.Furthermore, fast exposures, enabling imaging of moving workpieces maybe desired. All of these factors tend to reduce the amount of lightaccumulated during an image exposure, as discussed further below. Thus,a very high intensity flashlamp may be advantageous for providing a veryversatile machine vision inspection system.

The timing and synchronization portion 135 a may provide operations thatsend and receive control signals that synchronize the SLM 350, the lightgenerator 310, the camera 260 and positioning of the machine visioninspection system 10′. The SLM control portion 135 b may provide controlfor the various light channels by controlling the on-off timing,contrast, and aperture pattern, if applicable, of the SLM 350. The lightgenerator control portion 135 c may provide control for the powerlevels, the trigger signals, and on-off timing (if applicable) of theone or more lamps or LED's, or the like, of the light generator 310. Thelight generator control portion 135 c may also provide for light pathcontrol for auxiliary light sources (if applicable), as outlined furtherbelow.

FIG. 4 shows an exemplary SLM setup and control GUI 400 including an SLMimage field 410 and a control window 420. The SLM image field 410 showsone exemplary aperture pattern including a stage light channel aperturerepresentation 431, a coaxial light channel aperture representation 421,and PRL light channel aperture representations 441 a, 441 b, 441 c, 441d. The respective aperture representations may correspond to theapertures 321, 331, 341 a-341 d of the SLM 350, for example. The controlwindow 420 includes a stage light channel aperture control 531, acoaxial light channel aperture control 521, and PRL light channelaperture controls 541 a, 541 b, 541 c, 541 d, which control thesimilarly numbered aperture representations, and a set of correspondingcontrol signals that may be implemented to control the SLM 350. Forexample, when the SLM 350 is an LCD pixel array, the pixel array may becontrolled such that the gray-scale values that control the pixel arraycorrespond to the gray-scale values of the pixels shown in the SLM imagefield 410.

For the example shown in FIG. 4, the double cross-hatched backgroundrepresents a light-blocking region of the SLM 350. The stage lightchannel aperture representation 431 shows a similar doublecross-hatching to represent a significantly light-blocking setting ofthe corresponding control 531. The coaxial light channel aperturerepresentation 421 shows an unfilled area to represent a significantlylight-transmitting setting of the corresponding control 521. The PRLlight channel aperture representations 441 a, 441 b, 441 c, 441 d, showsingle cross-hatching to represent a partially light-transmittingsetting of the corresponding controls 541 a, 541 b, 541 c, 541 d. Thelayout of the aperture representations 421, 431, and 441 a-441 d in theSLM image field 410 may correspond directly to a physical layout of theapertures 321, 331, and 341 a-341 d of the SLM 350, and to a physicallayout of the input ends of the light cables 221, 231, and 241 a-241 d(FIG. 2), which may be held in a fixture proximate to the SLM 350, suchthat they are properly aligned to receive transmitted light from thecorresponding apertures. The particular layout shown in FIG. 4 isexemplary and is not limiting. Other configurations are possible andcontemplated. It will be appreciated that the various aspects ofaperture control described above with reference to FIG. 4, may alsogenerally be provided under manual, semi-automatic, or automatic controlas fuctions of the SLM control 135 b Accordingly, these and othermanual, semi-automatic, or automatic control measures over the apertures321, 331, and 341 a-341 d of the SLM 350 may be implemented to supportvarious learn mode and/or run mode operations of the machine visioninspection system 10′.

The control window 420 may include panels with the “slider” controlsoutlined above, along with corresponding numerical settings, along withother slider controls, numerical displays and radio buttons to adjustand display selected parameters which may control the light intensitiesof the various lighting channels and their representations in the SLMimage field 410. The PRL panel may include a “gang” PRL radio button 425that indicates whether the PRL sources 240 a. Through 240 d are gangedtogether, i.e., adjusted to the same setting, rather than separatelycontrolled.

The slider control scales may denote the range (from none to full) ofthe intensity to be transmitted by the corresponding aperture. Theslider control pointer and the numerical display may indicate theselected value to which the respective light source intensity may havebeen set. The numerical display may denote a digital quantity across abinary integer grayscale range of 2⁸ from full illumination at 255. Tono illumination at 0 In the example illustrated, the stage control panel531 shows, for example, a low-level value of 71, the coaxial controlpanel 521 shows, for example, a high-level value of 234, while all thePRL control panels 541 a-d show, for example, a mid-level value of 130.The PRL radio button 425 shows, for example, that the PRL sources areganged together in this example.

A background radio button 426 may indicate a selection of the displaybackground, being either white or black, shown in the example as beingblack (double cross-hatched.) In a set-up mode of operation, therespective slider controls of “Shift” scales 427V and 427H may be usedto adjust the position of the aperture pattern shown in the SLM imagefield 410 over a limited range along the vertical (V) and horizontal (H)directions, respectively. The actual location of the aperture pattern ofthe SLM 350 may be controlled in a corresponding manner. The alignmentof the actual aperture pattern of the SLM 350 relative to the physicallayout of the input ends of the light cables 221, 231, and 241 a-241 d.(FIG. 2), which may be held in a fixture proximate to the SLM 350, maybe monitored by direct observation, or by monitoring a lighttransmission signal through the various light channels or the like,until the various apertures have been properly aligned to the variouslight cable using the “Shift” controls. Then the corresponding“calibration” settings may be stored in the SLM control 135 b, for useduring ongoing operations of the machine vision inspection system 10′.

FIG. 5 shows an exemplary schematic layout diagram of the lightgeneration system 300, including light generator(s) 310 and a spatiallight modulator 350. A collimator lens 312 may receive light 314 fromone of a CW lamp 316, such as an HID lamp, or a Xe strobe 316′. Both mayhave substantially elliptical mirrors. A hinged mirror 313 may pivot toenable either the HID lamp 316 or the strobe 316′ to transmit lightthrough the collimator lens 312. In a first position 316 b, the lightfrom HID lamp 316 is blocked by the mirror 313, and the Xe strobe 316′may shine directly into the collimator lens 312. In a second position316 b′, the light from Xe strobe 316′ is blocked by the mirror 313, andthe light from HID lamp 316 may be reflected into the collimator lens312.

In either case, a light 314 may pass through the collimator lens 312,and be directed as collimated, or approximately collimated, light towardthe SLM 350. In the example shown in FIG. 5, the light 314 may passthrough an aperture 317, which may define the illumination area 315(FIG. 3), and may then pass through a filter 318 to block wavelengthsthat may contribute deleterious effects, such as undesirable heating, orimage blur, or the like. For example, in some applications, wavelengthsin the ultraviolet portion of the electromagnetic spectrum may focusdifferently than a dominant imaging wavelength and degrade images. Thelight may then pass, for example, through the previously discussedrespective apertures of the SLM 350 and into the respective opticalcables of the optical cable arrangement 319 that are aligned with therespective apertures, to be transmitted to the respective positions ofthe illumination sources 220, 230, and 240, for example. The input endsof the optical cables of the optical cable arrangement 319 may beinserted into an alignment and mounting plate (not shown) that has aplurality of holes that receive the ends of the optical cables and holdthem in an alignment that matches the aperture pattern of the SLM 350.The mounting plate may be mounted proximate to, or flush to, the SLM350, and may also act as an optical baffle or barrier between theoutputs of the various apertures and the optical cable ends, to reducestray light “cross talk” between the light channels. An alternativeconfiguration is shown in FIG. 9, described below.

FIG. 6 shows an exemplary bar chart 600 for the relative averagegrayscale intensity observed using a typical camera and constantillumination, for sundry workpiece surfaces at specific magnifications.Several materials, each at 1×, 2× and 6× magnification are listed alongthe abscissa 610, including floppy disk, brown connector, texturedmetal, green printed circuit board (PCB), integrated circuit (IC) lead,white connector, metal mirror and glass mirror. The 8-bit relativeaverage grayscale intensity along the ordinate 620 ranges from 0 through255, where zero is no intensity and 255 represents camera saturation oroverexposure.

As may be observed from the bar chart, increases in magnification reducethe amount of gathered light and the photographic exposure, andgenerally would demand greater quantities of light to provide sufficientphotographic exposure. Also, darker materials, such as the floppy diskmay require far greater quantities of light than brighter materials,such as the white connector, or specularly reflective materials, such asthe mirrors. This difference in the amount of exposure light receivedfor various materials and magnification demonstrates that the lightlevels that may be required for imaging and inspection of variousmagnified surfaces in a general purpose machine vision inspection systemmay vary widely. In fact, if the saturation values shown for thelow-magnification imaging of various materials are to be avoided, and ifthe low illumination values shown for the higher-magnification imagingof various materials are to be brought up to acceptable imaging levels,the illumination intensity may be required to be adjustable over a rangeof many orders of magnitude. Thus, there is a need for an illuminationsystem that provides an extraordinarily wide dynamic range and precisecontrol of available illumination.

To increase throughput, imaging the workpiece 20 disposed on the stage210 may be performed while the stage 210 remains in motion. Underselected conditions of image magnification and stage speed, a strobelight flash of high intensity and short duration may be required tosufficiently illuminate the workpiece 20 in a short enough exposure timeto avoid image blur during workpiece motion. To achieve a desirableillumination dynamic range with short illumination and/or exposuredurations, an extremely bright strobe lamp, such as a Xe lamp, may beadvantageous. For many types of lamps (which may also include LED's, orlasers, or the like, as the term “lamp” is used herein), after beingtriggered the strobe flash “profile” may temporally change in lightintensity beginning with a gradual initial rise, followed by a rapidincrease, a leveling off, a rapid reduction and a more gradual decay.Providing a reliable and consistent illumination exposure over a widedynamic range using such a flash profile would be desirable.

FIG. 7 shows an exemplary timeline chart 700 for trigger control of astrobe pulse and a camera integration period used for imaging. Theexposure level for an image may be determined by the transient lightlevel integrated by the camera over the exposure duration. The exposureduration may generally be limited by the strobe duration, or, when CWillumination or “long” illumination pulses are used, by the cameraintegration period. However, it is one goal of precision machine visioninspection systems to provide highly consistent precision metrologyimages that do not vary from workpiece to workpiece, such that edgemeasurements and the like, which form the basis for precisioninspection, do vary from workpiece to workpiece unless the workpiecestruly vary. Thus, in order to mitigate the changes in effective durationof the decay portion from one strobe flash to another, resulting inunacceptable variation in the total image exposure illumination, it maybe desirable to truncate the decay portion of the flash by ending thecamera integration period at a consistent time within the flash period.Furthermore, it should be appreciated that with a Xe lamp, for example,the ability to vary the flash duration may be limited, and the flashduration may be inherently less than a typical minimum cameraintegration period. Therefore, methods to reduce the effective exposureillumination provided by a strobe flash, by orders of magnitude, withconsistent control, may be desirable.

The chart 700 includes, for example, five timelines. The first timeline710 represents an image acquisition trigger signal 715 beginning at aposition trigger time T_(pta)based on positional X-, Y- and Z-axiscoordinates of the stage 210 (FIG. 2), which may correspond to aworkpiece feature being positioned in the field of view of the camera260.

The second timeline 720 represents a camera integration duration 725,that may have a programmable duration (T_(ei)-T_(si)) as short as tensof microseconds, and as long as several milliseconds. The controlledduration may be controlled based on a high-speed clock, such that it isrelatively consistent. The camera integration duration 725 may start atintegration begin time T_(si) and end at integration end time T_(ei). Insome implementations, the integration begin time T_(si) may occur adiscrete latency period (T_(si)-T_(pta)) after the position trigger timeT_(pta) has been used to initiate a camera integration period. However,the latency period may be relatively consistent.

The third timeline 730 represents the flash initiation signal 735beginning at a pulse trigger time T_(pt) to initiate the strobe flash.In some implementations, the pulse trigger time T_(pt) may be based bythe same high-speed clock that is used to determine the cameraintegration duration 725. Therefore, a pulse trigger delay period(T_(pt)-T_(si)) may be programmable, based on the high-speed clock, andrelatively consistent. The beginning of the pulse trigger time T_(pt)may initiate the strobe pulse flash intensity profile indicated by thefourth timeline 740. The flash intensity may exhibit a transientprofile, described further below, that rises to a peak 745 beforediminishing.

The fifth timeline 750 represents an exposure-related coordinateposition latch signal 755 beginning at latch time T_(txyz) that maycoincide with an effective or nominal exposure time. The X-, Y- and Z-coordinates for the stage 210 or the workpiece 20 at the latch timeT_(txyz) may be associated with the acquired image and may be stored inmemory 140. Descriptions of the timeline events, listed in order ofoccurrence during an image acquisition cycle, are summarized in Table 1below.

TABLE 1 Event No. Time Label trigger image acquisition 715 positiontrigger acquisition T_(pta) begin camera image 725 start integrationT_(si) integration (T_(si) → T_(ei)) strobe flash initiation 735 pulsetrigger T_(pt) flash pulse start start pulse T_(sp) flash peak intensity745 position latch signal 755 xyz coordinate assigned to T_(txyz) imageend camera image integration end T_(ei) integration (T_(si) → T_(ei))flash pulse end end pulse T_(ep)

The strobe pulse flash intensity profile begins at the pulse triggerT_(pt) with an initial gradual rise until effective start of the flashat time T_(sp). After a rapid rise to a peak value 745, the flash maythen diminish rapidly, to an effective end point of the flash at a timeT_(ep), and then continue to decay, providing little additionalillumination energy, as shown in FIG. 7. For a particular implementationand an particular lamp, a latency period between the pulse trigger timeT_(pt) and the effective pulse start time T_(sp) may be relativelyconsistent. Furthermore, for a given time period (T_(ep)-T_(sp)), theintensity profile and the illumination energy provided at a particularoperating voltage for a particular lamp may be relatively consistent.

As previously indicated, with a Xe lamp, for example, the ability tovary the flash duration (or profile) may be limited, and the flashduration may be inherently less than a typical minimum cameraintegration period. Therefore, to reduce the effective exposureillumination provided by a strobe flash, by orders of magnitude, withconsistent control, it may be desirable that the camera exposure end ata predictable and consistent time before the effective end time T_(ep)of the flash. As previously indicated, the pulse trigger delay period(T_(pt)-T_(si)) may be programmable, based on the high-speed clock, andrelatively consistent. Similarly, the programmable camera integrationduration (T_(ei)-T_(si)) may be programmable, based on the samehigh-speed clock, and relatively consistent. Furthermore, the latencyperiod between the pulse trigger time T_(pt) and the effective pulsestart time T_(sp) may be relatively consistent. Therefore, for a givenflash time period (T_(ep)-T_(sp)) and associated profile, the effectiveexposure illumination may be controlled by selecting and/or programmingthe programmable camera integration duration (T_(ei)-T_(si)), and thepulse trigger delay period (T_(pt)-T_(si)) such that camera integrationend time T_(ei) ends at a predictable time during the flash profile, andtruncates and determines the effective image exposure illumination. Thatis, to control the effective image illumination over a wide dynamicrange, the start of the effective image exposure illumination may beginwith the flash, a short time following the start of the cameraintegration period, and may end with the end of the camera integrationperiod, during the strobe flash profile. Of course, all of the abovelatency times may calibrated or determined for particular machines,lamps, voltage levels, etc., by design and/or experiment, and theresults calibrated or stored such that a combination of timing,operating voltages, and the like, that provide a desired or calibratedillumination level may be readily determined.

FIG. 8 shows an exemplary schematic block diagram including exemplarycontroller signals associated with portions of the control systemportion 120, the vision measuring machine 200 and the light generationsystem 300, shown in FIGS. 2 and 3. The control system portion 120includes the imaging control interface 131 that may comprise aframe-grabber, the motion control interface 132, and the SLM controlportion 135 b (FIG. 3). The motion control interface 132 may comprise amotion controller. The light generation system 300 may include the lightgenerator 310, the SLM 350 and an SLM interface portion 135 b′. Thetiming and synchronization portion 135 a may be located with, orpackaged in, the light generation system 300, which may facilitateretrofit applications of the light generation system 300.

The light generation system 300 may operate in conjunction with the SLMcontrol portion 135 b, the timing and synchronization portion 135 a(FIG. 3) and a video splitter 810. The timing and synchronizationportion 135 a and the SLM control portion 135 b. may be components ofthe light channel exposure and control portion 135 (FIG. 2). The visionmeasuring machine 200 (FIG. 2) includes the camera 260 and light sources220, 230, 240 to illuminate the workpiece 20. The coaxial mirror 233directs the light from the coaxial light source 230 toward the workpiece20.

The camera 260 may receive signals from the imaging control interface131, and may transmit image data via the imaging control interface 131via a video input 820. The camera 260 may also receive and transmitsignals between a serial communicator 830. A digital monitor 840 and/oran analog monitor 850 may display information related to the SLM 350(for example, as one means to implement the SLM setup and control GUI400, described with reference to FIG. 4). The SLM control portion 135 bmay supply SLM video signals to the video splitter 810 and the digitalmonitor 840. The video splitter 810 may supply video signals to thetiming and synchronization portion 135 a, and the SLM interface portion135 b′, as well as with the analog monitor 850. For example, the videosignal supplied to the SLM interface portion 135 b′ may be aconventional video signal, and the SLM interface portion 135 b′ mayreceive and decode the video signal into digital control signalssuitable for operating an SLM 350 that may comprise an LCD pixel array,to produce a desired aperture configuration and operating state.Generally, such SLM interface decoders are commercially available frommany vendors of LCD pixel array displays, such as the vendor of the LCDarray previously described.

The timing and synchronization portion 135 a may receive a positiontrigger output signal (for example, see 715, FIG. 7) from the motioncontrol interface 132 (conventional motion controllers may be programmedto provide such position triggers) and relay a related signal to theimaging control interface 131 (“OptoTRIG” in FIG. 8) to maintain thetiming relationships described with reference to FIG. 7. The imagingcontrol interface 131 may supply an exposure trigger signal to thecamera 260 to initiate the start of a camera integration period (forexample, see 725, FIG. 7) and supply a pulse trigger (for example, see735, FIG. 7) to the light generator 310, which may provide light to theSLM 350 for distribution to the light sources 220, 230, 240. The pulsetrigger signal may be delayed relative to the exposure trigger signal bya programmable amount, based on a high speed clock included in theimaging control interface 131. This programmable delay, in conjunctionwith the programmed integration period of the camera 260 (and, possibly,various consistent timing latencies) may be used to control theeffective image exposure illumination, as previously described withreference to FIG. 7. The high speed clock and the programmableintegration period and pulse trigger signal delay may be implemented invarious commercially available frame grabbers.

The timing and synchronization portion 135 a may supply a position latchtrigger signal (for example, see 755, FIG. 7) to the motion controlinterface 132, in order to latch the X-, Y- and Z- coordinates for thestage 210 or the workpiece 20 at a time that corresponds to theeffective image exposure time. For example, the timing andsynchronization portion 135 a may implement a latching time that bestcorresponds to the effective image exposure time based on the knownpulse trigger signal time and the known camera integration period, whichallows the timing of the effective image exposure period (for example,see T_(ei)-T_(sp), FIG. 7) to be known. For example, for short effectiveimage exposure periods, it may be sufficient for the position latchtiming to be set at the middle of the period (T_(ei)-T_(sp)). Or, for amore accurate effective image exposure time, the position latch time maybe set at the intensity-weighted average time of the period(T_(ei)-T_(sp)), based on the known flash intensity profile, which maybe determined experimentally, for example. The pulse trigger signal timethat is used to determine the effective image exposure time may bedetermined internally to the timing and synchronization portion 135 a,based on a delay related to the signal supplied to the imaging controlinterface 131 (“OptoTRIG” in FIG. 8), or, optionally, the pulse triggersignal time that is used may be determined based on sending the pulsetrigger signal in parallel to the synchronization portion 135 a, when itis sent to light generator 310.

Examples of selected components are described herein. The serialcommunicator 830 may represent an interface control tool. The controlsystem portion 120 may include a personal computer backplane with theSLM control portion 135 b provided by a Matrox dual video interface(DVI) daughter board and the imaging control interface 131 including aCorona II frame-grabber, both available from Matrox Electronic SystemsLtd, St-Régis Dorval (Quebec), Canada. The vision measuring machine 200may use Quick Vision™ controls for controlling the various lightsources. The SLM interface portion 135 b′ and the SLM 350 may beprovided by a micro-display graphics array and associated electronicsfrom CRL-Opto in Dunfermline, Scotland, United Kingdom. The motioncontrol interface 132 may include a motion controller, for example oneof the DMC-XXXX series of motion control cards commercially availablefrom Galil Motion Control, Rocklin, Calif., or a motion control cardsuch as that supplied as part of the previously described Quick Vision™systems.

FIG. 9 shows a schematic layout diagram of an alternate configuration ofthe light generation system 300′, including a light source channel thatprovides a structured light source 945. The light generation system 300′is generally similar to the light generation system 300 described withreference FIG. 5, therefore, only significant differences will bedescribed. In a first portion, the light 314 is provided, as previouslydescribed with reference to FIG.5.

The light 314 may be channeled, for example, through a fiber bundlelight conduit 910 to then pass, as collimated light 314′, through theaperture 317, the filter 318 and the SLM 350, which are located in asecond portion of the light generation system 300′. The second portionof the light generation system 300′ may include a hinged mirror 920,similar to the hinged mirror 313. In a first position 921 a, the light314′ may shine directly into the previously described optical cablearrangement 319, to provide all of the previously described illuminationfunctions.

Alternatively, the SLM 350 may be a controllable element that mayinclude, or be configurable or programmable to form, a structured lightpattern, in addition to the exemplary aperture patterns described above.For example, the structured light pattern may include a regular patternof light (light transmitting) and dark (light blocking) stripes at adesired pitch, and may be formed using the previously described LCDpixel array. In such a case, the collimated light 314′ that passesthrough the SLM 350 will may provide a field of parallel stripes oflight. In a second position 921 b, the hinged mirror may deflect theparallel stripes of light to pass through focusing and/or magnifying,and/or collimating lenses 930 before being emitted to provide astructured light source 945 that may be used to illuminate the workpiece20 (FIG. 2). The structured light source 945 may be mounted at a fixedand/or known position to emit the parallel light stripes toward theworkpiece 20 along an axis that is arranged at a known angle relative tothe optical axis of the machine vision inspection system 10′. Thus, animage 940 of the structured light pattern on the surface of theworkpiece 20 may be used in conjunction with known structured lighttriangulation techniques to determine relative dimensions of the profileof the workpiece 20 along the Z-axis direction. Various relatedteachings regarding the use of LCD arrays and structured lighttechniques are included in U.S. Pat. No. 6,690,474, which isincorporated herein by reference in its entirety.

It should be appreciated that in embodiments where the SLM 350 may beimplemented such that the various respective channel apertures may bepartially transmitting, for example, when the previously described LCDpixel array is used, the SLM 350 may advantageously be used to increasethe dynamic range of the effective image exposure illumination. That is,in addition to the dynamic range control provided by the previouslydescribed measures of controlling the camera integration period and thestrobe flash timing, gray-level control of an LCD pixel array, or acustom LCD element, or the like, may be used in parallel with any of theforegoing techniques, to provide additional illumination dynamic range.

Table 2 shows various factors which may be used in various combinationsto provide a desired illumination level, including the use of apartially-transmitting type of SLM. Row 1 shows that an LCD pixel arraymay provide a variable illumination attenuation that may be controlledwith an 8-bit gray-level command. However, in practice, the actual levelof variation observed in the transmitted light is limited toapproximately 150:1 Row 2 shows that an LCD pixel array may provide avariable “brightness” attenuation that affects all pixels at once, andmay provide an actual level of variation observed in the transmittedlight that is approximately 1.2:1 Row 3 shows that a Xe strobe lamp mayprovide a variable “brightness” depending on its operating voltagelevel, and may provide an actual level of variation observed in theprovided and transmitted light that is approximately 17:1 Row 4 showsthat a Xe strobe lamp generally provides an effective exposure time thatis shorter than a typical minimum camera integration period, therefore,for strobe exposures, the overall duration of the camera exposure periodis not used to affect the exposure. However, as previously indicated,the pulse duration may be set so as to stop the image exposure toeffectively truncate part of the flash profile. Row 5 shows that thepulse trigger delay (for example, see [T_(pt)-T_(si)], FIG. 7), whichgoverns the relative timing between the camera integration period andthe flash profile, may be adjusted in 40 ns time steps. That is, theflash profile may be selectively eliminated from the image exposure, in40 ns time steps. In practice, the actual level of variation observed inthe transmitted light by using this control measure may be approximately250:1 Rows 6 and 7 show factors which may vary from machine to machine,lamp to lamp, etc. Generally, it may be desirable to calibrate and/orcompensate these variations. Overall, according to Table 2, all of thesetechniques may be used in combination to provide an effective imageexposure illumination dynamic range of approximately 765,000:1 in a setof relatively precisely controlled and repeatable increments.

TABLE 2 Actual Adjustment Adjustment effect on Item Setting steps Unitsexposure Control Level 1 Pixel  0–255 DN 150:1 Individual lightbrightness (8 bit) channels (Individual (SLM) Pixels of SLM) 2 Display0x00–0x80 DN  1.2:1 All Light Channels brightness together (SLM) (EntireSLM at once) 3 Xe brightness 150–600 Volts Volt  17:1 All Light Channels(flash lamp) together 4 CCD exposure  0.1–250 10's of μs time None AllLight Channels (Tei-Tsi) (but stable together (Entire and camera atonce) Note: repeatable) No effect for strobe exposures. Strobe pulsetiming controls effective exposure time. 5 Pulse trigger  0–250 40 nstime time 250:1* All Light Channels delay steps together (Tpt-Tsi) 6Pulse rise time f(V_(FL)) None. Fixed time None Pulse delay vs. lampdelay or calibrated voltage is (Tpt-Tsp) characterized. Used tocompensate Tpt, if needed. 7 Xe pulse 10–30 None. Fixed μs None orcalibrated

FIG. 10 is a plot 1000 illustrating exemplary generic relationshipsbetween a light setting (power setting) during a continuous illuminationthat may be satisfactory during a reference or standard exposure time,and corresponding respective strobe duration times for a number ofrespective strobe light power levels represented by lines 1010, 1020,1030. When using the light generation system 300 or 300′ and the varioussystems and methods outlined above, particular strobe duration times maybe implemented by controlling the various timing relationships outlinedabove with reference to FIGS. 7 and 8.

The abscissa in FIG. 10 may correspond to the light setting (powersetting) during continuous illumination that produces a satisfactory“stationary” workpiece image that may be acquired throughout a referenceor standard exposure time, such as the frame rate of conventionalcameras. This method of illumination and exposure may be conventional,and may be well-suited for operation of a vision machine during manualoperations and training mode operations that involve a machine operator.The ordinate in FIG. 10 may correspond to a strobe duration timenecessary for a given strobe light power to achieve an image intensityequivalent to the light setting (power setting) during continuousillumination, that is, to achieve the same total exposure illuminationenergy for that light source.

A particular total exposure illumination energy may be defined ascorresponding to a particular continuous illumination level, when usingthe reference or standard exposure time. This energy may be divided by aparticular strobe light average power level that may directly determinethe corresponding required strobe duration time to a firstapproximation. Each of the exemplary strobe light power curves 1010,1020, 1030 may reflect a respective strobe lamp power setting consistentfor each point along the respective curves. Thus, operation according toany point along the higher power curve 1030 may allow a shorter strobeduration time than operation according to corresponding (verticallyaligned) points along either of the lower power curves 1020, 1010. Whenusing the light generation system 300 or 300′ and the various systemsand methods outlined above, higher strobe light power curves maycorrespond to higher strobe lamp operating voltages and/or controllingthe pixels of an LCD pixel array used for the SLM 350 to be fullytransmitting. Lower strobe light power curves may correspond to lowerstrobe lamp operating voltages and/or controlling the pixels of an LCDpixel array used for the SLM 350 to be only partially transmitting.

In order to provide the shortest possible strobe duration and produceimages having the least motion-related blur and the smallest possibleuncertainty in the elevation distance, there are advantages to operatingat a point toward the lower left end of any strobe light power curve.

Each strobe light source may inherently have a maximum allowable powerlevel and, in the absence of other camera response considerations, andother analogous devices, this factor may determine the fastest allowedstrobe duration. The higher power curve 1030 generally represents such amaximum power level. For a maximum or selected power level and a desiredoperating point, for example, as indicated by the line 1040, thecorresponding strobe duration period may then be determined.

The strobe duration period may provide the required matching totalexposure illumination energy. The lines 1050, 1060, generally representalternative settings for providing a desired illumination level by usingrespective strobe duration times corresponding to respective strobelight power levels. Also, for a desired strobe duration time definedalong the ordinate, the corresponding required strobe light power may bedetermined at the intersection of the abscissa and ordinate values inthe plot 1000.

An operator may input control parameters such as workpiece positions,light source intensity mixtures, etc. to inspect one or more workpiecesmanually, semi-automatically, or automatically. An example of types ofparameters that may be entered is shown in Table 3 below. Parameterssuch as workpiece image acquisition positions, stage velocity,magnification, light intensities, etc., may be provided.

TABLE 3 Parameter Name Parameter Value 1 Workpiece Position(s) X-, Y-,Z-coordinates 2 Stage Velocity V 3 Ring light: % of available power 100%or duty cycle 4 Coaxial light % of available power 75% or duty cycle 5Stage Light % of available power 50% or duty cycle 6 Magnification 1× 7Edge Position Tolerance or ±1.5 micron or ±0.25 pixels Allowable Blur 8etc. etc.

The parameters in Table 3 are only examples, and in particularsituations, more, or fewer, or alternate parameters may be necessary forcompatibility with different equipment designs.

The control parameters may be determined by an operator who places asample workpiece 20 (FIG. 2) onto the stage 210 (FIG. 2) and determinesthe best position, magnification, lighting, etc., with which to performthe image capture to obtain optimal results. An operator may image asample workpiece 20 with various parameter combinations and observe theimage captured by the camera 260 (FIG. 2) and assess whether the edgesare properly determined. After obtaining an operable set of parameters,the operator may enter those parameter values as programmed controlparameters.

The control system portion 120 may process the control parametersestablished by the operator that may be obtained during the staticimaging conditions of a training mode and convert them to appropriatecontrol commands for dynamic image capture during the continuous motionconditions of an automatic inspection mode. For example, successiveimage acquisition locations and the associated total illumination energyto be provided by each light source may be established by the operatorduring a training mode and the measurement path, velocities, SLMsettings corresponding to the various light sources, effective strobeduration period corresponding to the various light sources, etc, maythen be optimized by appropriate processing and/or analysis in thecontrol system portion 120 (FIG. 2), in order to yield the highestthroughput, or best accuracy, etc., during automatic inspection programexecution. After the dynamic image capture control commands for theautomatic inspection program have been generated, the control commands(and the control parameters) may be stored in the memory 140 for laterretrieval and use.

After processing the control parameters and/or retrieving controlcommands from the memory 140 (FIG. 2), the control system portion 120downloads image acquisition position parameters, the associated lightcontrol command information, and any other appropriate information tothe lighting control interface 133 and/or the light channel exposure andcontrol portion 135 and/or the light generation system 300 and maycontrol the other system components to execute an inspection process. Invarious applications, it may be desirable to use the dedicatedprocessing and deterministic timing of the light generation system 300in order to simultaneously control the high speed light pulse patternsof multiple light sources with sufficient accuracy, and at the desiredposition along a high-speed motion path. For example, the motioncontroller 132 may receive stage velocity information and command thestage 210 to move the workpiece 20 after receiving position informationfrom the light generation system 300, which may receive control commandsfrom control system portion 120 and processes the control commands intospecific data to control an image capture operation.

The captured images may be processed by the video tool portion 143. Theimage capture cycles may be repeated until completion of a total numberof inspection images for each workpiece 20 (FIG. 1), and the controlsystem portion 120 issues a next position signal corresponding to a next(if any) workpiece 20.

FIG. 11 is a flowchart illustrating an exemplary method 1100 of using ana strobe light source and a spatial light modulator to provide desiredillumination levels for one or more light sources in a machine visioninspection system. The operations shown in FIG. 11 may be executed, forexample, during learn mode operations of the machine vision inspectionsystem 10′, in order to determine various light control parameters thatmay to be used to provide strobe illumination during run modeoperations. The method may begin in step S1105 and proceed to stepS1110, wherein the light channel apertures of a controllable SLM may beset to correspond to one of more light sources selected by a user toilluminate a workpiece feature to be inspected. For example, for lightsources not selected by a user, the SLM may be controlled to set thecorresponding light channel apertures to an “OFF” condition. Theselected light channel apertures may be tentatively set to an “ON”condition. The method may then proceed to step S1120, wherein machinevision inspection system inputs the light power or intensity settingsthat are associated with the various selected light sources. The lightpower or intensity settings may be determined manually by a user, basedon observation of real time images while the user adjusts the lightsources during the learn mode operations, or automatically, based onmethods taught in U.S. Pat. No. 6,627,863, which is incorporated hereinby reference in its entirety. In some implementations, a light powersetting of zero may indicate an “OFF” setting for a light source, andsteps S1110 and S1120 may be merged or indistinguishable.

In step S130, the machine vision inspection system may analyze the lightpower or intensity settings input in step S1120 and determine timingrelationships between the strobe flash profile and the cameraintegration period, and/or a strobe lamp operating voltage, based on thelight power or intensity settings, such that the strobe illuminationthat is integrated during the camera integration period provides anillumination level that is sufficient for all of the respective selectedlight source channels, in comparison to their respective light power orintensity settings. The control parameters corresponding to thedetermined timing and/or voltage level may be stored in memory and/orimplemented in the appropriate circuits or routines. The correspondingstrobe illumination level may exceed the respective light power orintensity settings for some or all of the light source channels, if acontrollable SLM is available to attenuate the light transmission to thevarious light source channels. In a decision step S1140, it may bedetermined whether the timing and/or voltage level determined in stepS1130 is sufficient to provide the desired light power and/or intensitysetting for each selected light source. If so, then operation mayjump tostep S1160. Otherwise, operation proceeds to step S1150. In step S1150,the respective light channel apertures are adjusted in the SLM toprovide respective partial light transmission settings and/or respectiveaperture sizes that provide a level of light transmission attenuationthat provides the desired light power and/or intensity level for eachrespective light channel. It should be appreciated that a light channelaperture size can be reduced in the SLM, instead of, or in addition toadjusting the pixel gray-levels or the like, in order to attenuate thelight transmission through a light source channel aperture. It should beappreciated that in the step S1150, the SLM may be adjustedindependently for each light source channel aperture, such that onestrobe flash can be differently attenuated for each respective lightsource channel, to provide a desired combination of illumination levelsfor multiple light sources during a single flash.

In an optional step S1160, the light control settings determined insteps S1130-S1150 may be tested by acquiring and evaluating a workpieceimage using the settings. For example, the user may observe theresulting image on a display of the machine vision inspection systemduring learn mode, and accept or reject the image. If the image isrejected, the light control settings may be refined and retested untilan acceptable image results. However, if the image illumination is notcritical for a particular image, and/or if the various light controlsettings are adequately accurate and/or calibrated such that reliableillumination levels are obtained without confirmation of the determinedsettings, then the step S1160 may be omitted. In step S1170 the finallight control settings determined in steps S1130-S1160 may be applied toacquire a workpiece image suitable for learn mode inspection operationsand/or recorded, for example, in a part program that may be used laterfor automatic high-speed inspection. The process may then end in stepS1175.

Artisans having skill in the art will recognize and understand thatvarious functions for the systems and methods for controlling strobeillumination may be performed in any manner among any quantity (e.g.,one or many) of hardware and/or software modules or units, computers orprocessing systems or circuitry. The control system portions may beintegrated within a stand-alone system or may be executed separately andbe coupled to any number of devices, workstation computers, servercomputers or data storage devices via any communications medium (e.g.,network, modem, direct connection, wireless transmission).

The control system processes may be implemented by any quantity ofdevices or processing systems (e.g., IBM-compatible, Apple, Palm Pilot,Blackberry). The computer system may include any commercially availableor customized operating system (e.g., Windows, Macintosh, Unix, Linux,OS/2, DOS) to execute any commercially available or custom designedsoftware (e.g., Quick Vision™) and any type of input devices (e.g.,keyboard, mouse, microphone, I/O port, wireless receiver). It is to beunderstood that the software of the strobe illumination control may beimplemented in any desired computer language (e.g., C, C++, Java,Fortran, Lisp, SQL), and could be developed by one of ordinary skill inthe computer and/or programming arts based on the functional descriptioncontained herein. Moreover, such software may be available ordistributed via any suitable medium (e.g., stored on magnetic or opticaldevices such as CD-ROM and diskette), downloaded from the internet orother network, downloaded from a bulletin board, or other conventionaldistribution mechanisms.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

1. A system for controlling image exposure strobe illumination used toilluminate a workpiece such that the workpiece may be imaged by a camerain a machine vision system, the system comprising: a camera operable toprovide a camera image of the workpiece; a strobe light generator thatemits radiation usable by the camera for imaging; a controllable spatiallight modulator configured to provide a first controllable light channelaperture positioned to receive a first portion of the emitted radiationand to control an amount of the first portion of the emitted radiationwhich it outputs as first channel light, and a second controllable lightchannel aperture positioned to receive a second portion of the emittedradiation and to control an amount of the second portion of the emittedradiation which it outputs as second channel light; a control systemportion that controls the spatial light modulator; and at least firstand second light channel light cables, wherein: the first light channellight cable comprises a first optical fiber bundle, and has an input endpositioned to receive the first channel light through the first lightchannel aperture, and is configured to output the first channel lightthrough a first light source that projects first channel illuminationfrom a first position relative to the workpiece; the second lightchannel light cable comprises a second optical fiber bundle, and has aninput end positioned to receive the second channel light through thesecond light channel aperture, and is configured to output the secondchannel light through a second light source that projects second channelillumination from a second position relative to the workpiece; the firstlight channel aperture comprises a first portion of the spatial lightmodulator that is controllable to provide at least three respectiveconfigurations which respectively minimally attenuate at a minimalattenuation level, partially attenuate at a partial attenuation levelthat is greater than the minimal attenuation level, and substantiallyblock at a full attenuation level, the amount of emitted radiation whichit outputs as first channel light during a strobe flash; and the secondlight channel aperture comprises a second portion of the spatial lightmodulator that is controllable to provide at least three respectiveconfigurations which respectively minimally attenuate at a minimalattenuation level, partially attenuate at a partial attenuation levelthat is greater than the minimal attenuation level, and substantiallyblock at a full attenuation level, the amount of emitted radiation whichit outputs as second channel light during a strobe flash.
 2. The systemaccording to claim 1, wherein the first and second light sources areconfigured such that the first channel illumination and the secondchannel illumination each illuminate an entire camera image of theworkpiece.
 3. The system according to claim 1, wherein the controllablespatial light modulator is configured to provide the first and secondcontrollable light channel apertures at a first time, and is configuredat a second time to provide a structured light pattern positioned toreceive the emitted radiation, and to output the emitted radiation in aform of a corresponding structured light which is transmitted toilluminate the workpiece.
 4. The system according to claim 1, whereinthe first portion of the spatial light modulator comprises at least onetransmissive element that is controllable to provide at least threerespective levels of attenuation corresponding to the minimal, partialand full attenuation levels.
 5. The system according to claim 4, whereinthe at least one transmissive element comprises an LCD element.
 6. Thesystem according to claim 4, wherein the at least one transmissiveelement comprises a plurality of elements.
 7. The system according toclaim 6, wherein the respective configuration that provides the partialattenuation level comprises controlling some of the plurality ofelements at the full attenuation level to, in effect, reduce the size ofthe first light channel aperture that outputs the first channel light.8. The system according to claim 7, wherein the respective configurationthat provides the partial attenuation level comprises controlling someof the plurality of elements at the partial attenuation level to, ineffect, partially attenuate transmission through the reduced size of thefirst light channel aperture that outputs the first channel light.